The Sam domain of the lipid phosphatase Ship2 adopts a common model to interact with Arap3-Sam and EphA2-Sam

Background: Sterile alpha motif (Sam) domains are small protein modules that can be involved in homotypic or heterotypic associations and exhibit different functions. Previous studies have demonstrated that the Sam domain of the lipid phosphatase Ship2 can hetero-dimerize with the Sam domain of the PI3K effector protein Arap3. Results: Here, we determine the NMR solution structure of Arap3-Sam and implement a multidisciplinary approach consisting of NMR spectroscopy, ITC (Isothermal Titration Calorimetry), mutagenesis and molecular modeling studies to analyze the interaction between Ship2-Sam and Arap3-Sam. This work reveals that Arap3-Sam may associate with Ship2-Sam by adopting a binding mode common to other Sam domains. This binding mode is identical to what we have very recently observed for the association between Ship2- Sam and the Sam domain from the Ephrin A2 receptor. Conclusion: Our studies further clarify the structural features that are relevant for Sam-Sam interactions involving Ship2 and give additional hints that could be used for the identification of new molecules able to selectively inhibit Sam-Sam associations.